Research On The Operating Performance Of Air Source Heat Pump In Low Temperatures

There are some shortages of air source heat pump system in low temperature environment, such as difficulty in starting,high compression ratio, low heating capacity, frequently defrosting,and so on,so the application of air source heat pump is limited in cold area in northern China. Many scholars and business have been investigating the operating characteristics of air source heat pump. In this paper,the operating characteristics of air source heat pump was investigated and the problems of its operating characteristics was researched from the principle, the operating conditions and other aspects,and solutions to improve the applicability of air source heat pump was found:An supplementary air source heat pump with a sub-cooler was proposed,which was contrasted with no comparative analysis,and mathematical models of the two units was established,and simulation calculations of the two units was carried out. Among them,the method of calculation for the air source heat pump with increased enthalpy was that the operational parameters was calculated with different pressures and weights, refering to the intermediate pressure in different evaporating temperatures and the best quantities of the feeding pressur and the feeding vapor.It was indicated that the discharge tempreture for compressor of the supplementary heat pump was lower than the general one,and the heating capacity of the former was better than the latter,and the difference of heating capacities of the two units tended to increase with the increasing evaporation temperature.The cop of the supplementary heat pump was reduced when the evaporation temperature was in -25℃～-15℃,and the cop of the supplementary heat pump was lower than the general one when the evaporation temperature was higher than -15℃,so the advantages in heating capacity of the supplementary heat pump was diminished. The application of the supplementary heat pump was tested and the consequence was compared with its simulation results,and the residual was reasonable,so the calculation conclusion was verified by the tests.A sub-critical CO2 tender of two-stage coupling air-source heat pump,in which CO2 as the refrigerant of low- temperature compression and R22 as the refrigerant of high- temperature compression.It had three operation modes:two-stage heating operation mode in wenter, single -stage heating operation mode in wenter and single-stage refrigeranting operation mode,and they could be achieved. Mathematical models of the unit was established,and simulation calculations of the unit was carried out,which indicated that its discharge tempreture for compressor was reasonable when evaporation temperature was -40℃,and the heating capacity of the unit tended to increase with the increasing evaporation temperature,the cop was maximum 1.72 when the evaporation temperature was -25℃. The consequence was compared with the supplementary heat pump,and the advantages and their suitable tempretures,which provided a theoretical basis for further study.A energy-storage defrosting air source heat pump was proposed,which had the functions of quickly starting and energy-storage defrosting.And the model machine was manufactured for the testing of the applications of its starting and defrosting characteristics.The results show that the starting characteristic could be improved and the running time of defrosting could be reduced,so the indoor thermal condition was improved.